I have a Canon 430EX flash and an iPhone 5. I really enjoy the quality of the camera in daylight, but of course in low light conditions the built in LED flash is quite poor. So would it be possible to use an off camera flash such as the one I have to provide additional light for the camera? I would prefer to use this in practice and not just for theoretical purposes.

Very nice link @tenmiles. My brother used to have that p&s....
– FrancescoOct 7 '12 at 8:42

Do we know what settings he used on the 430 EX II for this? I have that flash and an iphone, and am very interested!!! :)
– MikeOct 9 '12 at 9:03

1

I don't think it will work with the iPhone, though, because it has an LED rather than a proper flash.
– mattdmOct 12 '12 at 2:45

@mattdm - You are correct. There are two issues with this answer. First of all the 430EX does not have an optical sensor(unlike the Nikon flash used in the video linked to). And secondly all of the smart phones I have tested do not seem to trigger flashes optically. What exactly the reason is for that I'm not sure but in any case it doesn't work.
– dpollittMay 29 '14 at 3:23

If there's some consistency in the time between when a phone turns on it's LED "flash" and when the exposure happens, it seems like you could design a sensor with an adjustable lag and tune it by trial-and-error... but you would still have to be able to tell the camera not to crank up ISO somehow.
– junkyardsparkleFeb 20 '15 at 23:13

The iSyncFlash app is supposed to do this, by syncing the iPhone's camera to the flash, rather than the other way around (although the current reviews of the app indicates it doesn't work much on phones newer than a 4s). And you may be able to accomplish this with TriggerTrap Mobile, two Android/iOS devices, and a flash adapter; TriggerTrap Mobile uses the headphone jack for the sync signal.

3 years ago I bought a nova flash for iPhone and have been using it ever since with great success. it fits in a credit card slot in my wallet and works with the Nova app. You can also use more then 1 if you wish to have multiple flashes. Great option for extra light and the app is very good with editing tools and presets. Battery last a very long time and it turns on via BT as soon as you open the app. There is no switch on the flash itself. there are different setting for the typ of light and intensity. I love my Nova.